Basic sulfurized calcium alkylphenates are used as compounding agents or additives in lubricating oils to neutralize harmful acids in internal combustion engines and to inhibit corrosion, gum formation and piston ring sticking caused by oxidation of the lubricating oil and oxidative polymerization of the engine fuel residues. Metal sulfonates are commonly used in lubricating oil compositions as additives, rust inhibitors and detergents. It is highly desirable for such phenates or sulfonates to provide neutralization capacity for acids formed in engine combustion without too rapid loss in alkalinity. In some cases, these compounding agents or additives are overbased, containing a molar excess of base over that needed to neutralize the phenolic material or sulfonic acid.
A problem associated with the preparation of overbased additive compounds is that of the incompatibility of the mixture of the alkaline earth metal phenate and the sulfonate as a final product. The overbased materials, generally an alkaline earth metal compound, generally a carbonate, are dispersed in the alkaline earth metal dispersing agent, the amount of dispersed alkaline earth metal being known as the overbased amount. Since the greater the basicity of the material the better, as this allows smaller amounts of the material to be used for a given effect in a lubricant, a greater degree of overbasing is highly desirable. However, to increase basicity, it is generally necessary to increase the dispersed alkaline earth metal content of the carbonate complex.
A highly desirable object of overbasing additive agents is to obtain the overbased additive agents in the form of extremely fine particles in a finely dispersed colloidal form such that the lubricant compositions containing the overbased additive agents are stable, are haze-free, are gelatin-free and are not subject to appreciable thickening.
The instant invented process relates to increased both carbonation and sulfurization of an alkaline earth metal phenate in the presence of a low-based sulfonate promoter to give a resulting product with improved water tolerance, due to overcoming incompatibility of the phenate and sulfonate.
Overbased phenates, including sulfurized phenates, are commonly manufactured in the presence of ethylene glycol which must be removed from the product. The presence of glycol in overbased phenates can cause engine varnish or lacquer. Phenates are generally the reaction product of phenol or substituted phenol with a metal or ammonium base. Often the metal base is a Group II metal compound. Substituted phenols are generally mono-, di- or tri-hydrocarbyl substituted, such as alkyl, alkenyl, aryl, aralkyl, or alkaryl. Monoalkyl substitution is preferred. The hydrocarbyl can comprise low molecular weight groups such as methyl, ethyl, the isomers of propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl and the like up to high molecular weight materials having a number average molecular weight of 10,000 or more. These hydrocarbyl substituents can be intermediate molecular weight polymer olefins such as C.sub.8 -C.sub.100 ethylene or propylene or butene polymers. The hydrocarbyl can be substituted with groups such as chlorine, bromine, hydroxy, nitro or sulfonic acid groups so long as such substitution does not interfere with the utility of the composition. The Group II metal compound can comprise a metal oxide, hydroxide, alcoholate, acetate and the like. Common metals are calcium, barium, strontium and magnesium. Often, the metal compound is calcium oxide or hydroxide. Phenates can contain sulfur which can be introduced by reaction of elemental sulfur or SCl.sub.2 with phenol or substituted phenol, or by reaction of elemental sulfur or SCl.sub.2 with metal phenate.
Methods of making these various phenates and sulfur containing phenates and overbasing can be found in U.S. Pat. Nos. 2,680,096; 3,036,971; 3,178,368; 3,336,224; 3,437,595; 3,464,970; 3,761,414; 3,801,507; 3,810,837; 3,923,670; 3,932,289; 3,953,519; 3,966,621 and 3,969,235.
As is well-known, calcium phenates having TBN's of 80-250 tend to interact with low and high base sulfonates to produce haze and sediment when blended into crankcase oils. This phenate-sulfonate incompatibility can be influenced by the components in a finished oil. For example, the simultaneous presence of zinc dialkyldithiophosphate (ZnDTP) and water can aggravate the phenatesulfonate interaction. Many finished oils contain ZnDTP. This phenate-sulfonate incompatibility is worsened when the finished oil contains a small amount of water, as can happen during handling and storage.
It has long been known, as evidenced by U.S. Pat. Nos. 4,293,431; 4,302,342 and 4,412,927, that an overbased metallic detergent-dispersant can be prepared by carbonating a sulfurized alkylphenate of an alkaline earth metal, an alkaline-earth metal alkylbenzene sulfonate, an alkaline-earth metal compound, an alkylene glycol and a diluent oil. These approaches, however, utilize a significant amount (&gt;20 wt % based on phenate) of sulfonate for the phenate overbasing reaction. This obviously reduces the effective reactor volume for the phenate reaction and the resulting product loses flexibilities in its applications.
In our process, we have found that only a small amount (&lt;10 wt% and preferably &lt;5 wt %) of low-based sulfonate is required as a promoter for alkaline earth metal phenate reactions in the presence of an alkylene glycol and a diluent oil. These sulfonate promoted phenates in an overbased state have improved solubility in lubricating oils, particularly in the presence of small amounts of water, are stable colloidal dispersions, are haze-free, are gelatin-free, non-viscous and are not subject to appreciable thickening. We have also found that optimization of both sulfurization and carbonation provides improved water tolerance in lubricating oil additives.